A. M. Kulkarni

Control design and simulation of unified power flow controller

The unified power flow controller (UPFC) is a solid-state controller which can be used to control active and reactive power flows in a power transmission line. In this paper, the authors propose a control strategy for UPFC in which they control real power flow through the line, while regulating magnitudes of the voltages at its two ports. They design a controller for this purpose which uses only local measurements. The control strategy is evaluated using digital simulation for a case study.

Power oscillation damping using FACTS devices: modal controllability, observability in local signals, and location of transfer function zeros

Modal controllability, observability, and transfer function zeros play an important role in the selection of candidate locations and feedback signals for flexible ac transmission systems (FACTS)-based power swing damping controllers. This paper investigates location of zeros of the transfer function corresponding to FACTS devices and certain local feedback signals. Signals synthesized from locally measured signals are derived that can give good pole-zero separation. It is also shown that relative modal controllability of FACTS controllers at various locations can be directly inferred from relative modal observability in certain signals at those locations. These signals are identified for various FACTS devices. Case studies using detailed model are used to validate the results.

Stability-constrained generation rescheduling using energy margin sensitivities

In this paper, a structure preserving energy margin (EM) sensitivity-based analysis is presented to determine the amount of preventive generation rescheduling to stabilize a transiently unstable power system. An expression using a simplified model is derived to relate the change in the EM to change in generation. Utilising this expression, two approaches for generation rescheduling are developed which are applicable to detailed model of power systems. The proposed methods are applied to the 10-machine New England power system and 16-machine power system with detailed power system models.

Determination of effectiveness of transient stability controls using reduced number of trajectory sensitivity computations

This paper presents a new approach for determining the effectiveness of preventive generation rescheduling and shunt/series compensation in improving transient stability using trajectory sensitivity (TS) method. It is shown that the effectiveness of changes in parameter values can be judged by evaluating the TS of certain variables with respect to clearing time. Therefore, the need to evaluate a host of sensitivities with respect to many parameters is obviated. This heuristic is motivated by the fact that for simple models and small changes, controllability of trajectories using certain parameters can be inferred from observability in certain output signals. An example of such a parameter and signal pair is shunt susceptance at a bus and the square of voltage at that bus, respectively. Case studies are carried out on a 10-machine 39-bus system with detailed models and 17-machine system to validate this method.

Analysis of SSR Performance of TCSC Control Schemes Using a Modular High Bandwidth Discrete-Time Dynamic Model

Subsynchronous resonance (SSR) performance of various control schemes of a thyristor controlled series compensator (TCSC) has been studied in the previous literature using digital simulation based analyses. With the availability of a modular, high bandwidth (six-sample per cycle), discrete-time model of a TCSC, accurate eigen-analysis of a TCSC compensated system has become feasible. Therefore, we revisit the issue of SSR performance in order to gain additional insight provided by this analytical model. We use the model to assess fixed firing angle delay (FFAD) and synchronous voltage reversal (SVR) under different situations. The performance of synchronization schemes and an output feedback subsynchronous damping controller (SSDC) is also evaluated. The derivation of the model is outlined and validated by comparing the results of eigen-analysis with those obtained by detailed digital simulation.

Damping of power swings using series facts controllers

The main aim of this paper is to identify optimal control laws and locations of series connected FACTS controllers (like TCSC and SSSC) in a unified framework to damp power swings. A circuit analogy of the electro-mechanical system is used to suggest the control laws and a location index is also proposed. The signals which are used can be synthesized using locally available measurements. The method is validated on a detailed model of a 3-machine and a 10-machine system.

Decentralized sliding mode control technique based power system stabilizer (PSS) for multimachine power system

Power system stabilizers (PSSs) are added to excitation system to enhance the damping of low frequency oscillations. In this paper, the design of PSS for multimachine power system (MMPS) using output feedback sliding mode control is proposed. The nonlinear model of a multimachine power system is linearized at various operating points and the linearized model of the plant is obtained. The multirate output feedback sliding mode controller is designed and is applied to nonlinear plant model of the multimachine power system at those operating (equilibrium) points. This method does not require the complete states of the system for feedback and is easily implementable

Design of power system stabilizer for single machine system using robust fast output sampling feedback technique

Abstract Power system stabilizers (PSS) are added to excitation systems to enhance the damping during low frequency oscillations. In this paper, the design of PSS for single machine connected to an infinite bus using fast output sampling feedback is proposed. The non-linear model of a machine is linearized at different operating points and 16 linear plant models are obtained. For all of these plants a single stabilizing state feedback gain, F is obtained. A robust fast output sampling feedback gain which realizes this state feedback gain is obtained using linear matrix inequalities approach. This method does not require state of the system for feedback and is easily implementable. This robust fast output sampling control is applied to non-linear plant model of one machine at different operating (equilibrium) points. This method gives very good results for the design of PSS.

Dynamic Phasor Analysis of SSR Mitigation Schemes Based on Passive Phase Imbalance

This paper presents the application of dynamic phasor analysis to understand the effect of passive phase imbalance schemes on the torsional modes of a turbine-generator system. These schemes have been proposed in the previous literature as subsynchronous resonance (SSR) countermeasures. Dynamic phasor analysis of the unbalanced system yields a linearized and time-invariant model which facilitates eigen-analysis. It is seen that large levels of phase imbalance can cause a significant movement in the subsynchronous network modal frequencies. Therefore, in specific cases, SSR can be avoided due to detuning of the torsional and network modes. However, the analysis also shows that damping torque in a series compensated network is negative at subsynchronous frequencies even with phase imbalance. Therefore, phase imbalance cannot be a general countermeasure to the problem of SSR.

Robust decentralized fast-output sampling technique based power system stabilizer for a multi-machine power system

Power-system stabilizers (PSSs) are added to excitation systems to enhance the damping during low-frequency oscillations, In this paper, the design of robust decentralized PSS for four machines with a 10-bus system using fast-output sampling feedback is proposed. The nonlinear model of a multimachine system is linearized at different operating points, and 16 linear state space models are obtained. For all of these plants, a common stabilizing state feedback gain, F, is obtained. A robust decentralized fast-output sampling feedback gain which realizes this state feedback gain is obtained using LMI approach. This method does not require all the states of the system for feedback and is easily implementable. This robust decentralized fast-output sampling control is applied to a nonlinear plant model of several machines at different operating (equilibrium) points. This method yields encouraging results for the design of power-system stabilizers.